1. Field of the Invention
The present invention relates to an image forming apparatus that is suitably usable for a copying machine, a printer, a plotter, a facsimile machine, or the like.
2. Description of Related Art
One image forming apparatus that has been conventionally known is disclosed in U.S. Pat. No. 3,689,935 in which an electrode having plural opening portions (hereinafter referred to as xe2x80x9caperturesxe2x80x9d) is used, and a voltage is applied to the electrode in accordance with image data to control passage of toner particles through the apertures, whereby an image is formed on a supporter (image receiving medium) with toner particles that have past through the apertures.
The image forming apparatus includes an aperture electrode unit comprising an insulating flat plate, a reference electrode formed continuously on one surface of the flat plate, plural control electrodes that are formed on the other surface of the flat plate and that are electrically insulated from one another, and at least one row of apertures each of which is formed in correspondence with each control electrode so as to penetrate through the flat plate, the reference electrode and the control electrodes. The image forming apparatus also includes structure for selectively applying a voltage across the reference electrode and the control electrodes, structure for supplying charged toner particles so that the flow of the toner particles passed through the apertures is modulated in accordance with the applied voltage, and structure for moving a supporter and the aperture electrode unit relative to each other to position the supporter in a particle flow passage.
U.S. Pat. Nos. 4,743,926, 4,755,837, 4,780,733, and 4,814,796 disclose image forming devices having an aperture electrode unit disposed so that control electrodes face a supporter and a reference electrode faces a toner supply side.
On the other hand, U.S. Pat. No. 4,912,489 discloses an aperture electrode unit disposed so that the reference electrode faces the supporter and the control electrodes face the toner supply side. The reference describes that a voltage to be applied to the control electrodes at an off-time can be reduced to about a quarter of that of the image forming apparatus as disclosed in the above patents.
The term xe2x80x9coff-timexe2x80x9d means a time when no toner particle is attached onto the supporter, that is, when a blank portion of an image is formed on the supporter, and conversely, the term xe2x80x9con-timexe2x80x9d means a time when a toner image is formed on the supporter.
However, in the conventional image forming apparatus as described above, each aperture is controlled in accordance with a voltage to be applied to each control electrode, and thus, there is a problem that the cost of the driving circuit is high. For example, an A4-size aperture electrode unit having 200 DPI resolution is provided with 1728 apertures, and thus, driving circuits whose number is equal to the number of the apertures are required to drive all the apertures independently of one another. Particularly, a driving circuit using a driving voltage exceeding 40 volts is very expensive, and it is therefore impractical to use a number of these expensive circuits. Further, a higher resolution of about 600 DPI is becoming more popular in the market, and in order to realize the high 600 DPI resolution, an even larger number of apertures must be provided in the aperture electrode unit. Therefore, the problem is worsening.
An object of the present invention is to provide an image forming apparatus that is capable of performing a recording or printing operation at a high resolution with a small number of driving ICs and that is low in cost.
In order to attain the above object, the image forming apparatus according to the present invention includes a carrier for carrying charged particles, an electric-field controller that is disposed so as to face the carrier and for directly controlling the charged particles with an electric field, and a back electrode that is disposed so as to face the carrier through the electric-field controller. The electric-field controller has openings through which the charged particles pass. The apparatus also includes a plurality of electrode units that are disposed adjacent the openings, the plurality of electrode units being time-divisionally driven.
In the image forming apparatus of the present invention thus constructed, the plurality of electrodes are time-divisionally driven, and an electric-field control operation is effectively performed. Accordingly, for example, if data electrodes and selection electrodes are used, an image recording operation can be properly performed because both of the electrodes can provide sufficient toner flying (supplying) force to the toner, and in addition, the number of driving ICs can be reduced, resulting in a reduction of cost.
In a preferred embodiment, the data electrode is adjacent at least two of the plurality of openings, and the selection electrode is adjacent at least one of the plurality of openings. The data electrode controls the charged particles passing through the at least two of the plurality of openings.